Search by email address
A service telling if one's login details has been hacked on different services. You can use it to check out other people's email addresses to see what services they have registered for.
KnowEm lets you control the use of personal names or usernames directly on over 500 popular and new social media. Choose between SearchUsername, CheckUsernames och Namechk
A tools to search domain and social username availability. Helps identifying on what services a user is registered.
Namechk is a free username and domain search tool. Helps identifying on what services a user is registered. Users can sort results in many different ways, including only available networks, by rank and developer-focused networks. Once you’ve sorted your results, you can download to a CSV file in order to guide your registration process.
Good page to check out different usernames and the services they are associated with.
Tools to check people in social media. Check out their advanced search for APIs.
Search tool from IntelTechniques
Social Media Investigations - name, phone, email, username searches.
Checking phone numbers and what social media they are attached to.
Checking phone numbers
Tool to find personal details, addresses & criminal records of US citizens
Reverse username search